1. Field of the Invention
The present invention relates generally to data storage and more particularly to maximum data storage in a magneto-optical data storage system.
2. Background Art
Hard disk technology has historically been limited by conventional magnetic head designs. A typical prior art Winchester magnetic storage system includes a magnetic head that has a slider element and a magnetic read/write element and is coupled to a rotary actuator magnet and coil assembly by a suspension and actuator arm so as to be positioned over a surface of a spinning magnetic disk. In operation, lift forces are generated by aerodynamic interactions between the magnetic head and the spinning magnetic disk. The lift forces are opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
Flying head designs have been proposed for use with magneto-optical (MO) storage technology. One motivation for using magneto-optical technology stems from the higher areal density capabilities of magneto-optical storage disks. However, despite the historically higher areal storage density available with MO storage technology, the prior art MO disk drive volumetric storage capacity has generally not kept pace with the volumetric storage capacity of magnetic disk drives.
One factor that continues to limit MO disk drives is the physical size of the head necessary to hold the various components required for accessing magneto-optical information. Conventional magneto-optical heads, while providing access to magneto-optical disks with areal densities on the order of 1 Gigabit/in.sup.2, have been based on relatively large optical assemblies, which have made the physical size and mass of the heads rather bulky (typically 3-5 mm in a dimension).
A number of flying MO head designs incorporating magnetic and optical elements are described in U.S. Pat. No. 5,295,122 by Murakami, including: use of free-space alignment of a laser beam with a dynamically moving target, and a number of different configurations of the magnetic and optical elements that are required for reading and writing using the magneto-optical Kerr effect. The large size, mass, and number of elements limits the minimum head size and, therefore: the speed at which information from the MO disk may be accessed, the tracking bandwidth, and the data density that may be read or written. In the prior art, the large physical size of MO flying heads also limits the spacing between magneto-optical disks to a finite minimum value. Consequently, because the volume available in standard height disk drives is limited, magneto-optical disk drives for use with magneto-optical flying heads have generally not been available as high capacity multi-platter commercial products.
During conventional writing of information in MO disk drives, an incident laser beam heats a selected spot of interest on the MO disk to approximately the Curie point. A time varying vertical bias magnetic field is used to define a pattern of "up" or "down" magnetic domains in a recording layer. Subsequently, as the selected spot of interest cools, information is recorded on the MO disk. The size of the magnetic field that is generated provides a lower limit on a maximum data density that may be recorded on the MO disk. One prior art approach for generating the necessary magnetic field for writing of information has relied on second surface recording techniques. With the second surface recording method, the magnetic field is applied to the spot of interest on the MO disk from a direction opposite that of the incident laser beam. With this approach, only one side of a MO disk may be used.
In addition to the aforementioned limitations, information access in prior art magneto-optical storage systems is limited by the size of the optical spot to which an incident laser beam may be focused on the disk surface. Magneto-optical information access requires the use of polarized laser light for reading and writing information on an MO disk. In the case of reading information, MO technology makes use of a magneto-optical effect ("Kerr" effect) to detect a modulation of polarization rotation imposed on the linearly polarized incident laser beam by the recorded domain marks in the recording layer. The polarization rotation (representing the information stored at recorded marks or in the edges of the recorded marks) is embodied in a reflection of the linearly polarized laser beam and is converted by optics and electronics for readout.
To date, only conventional quadrilayer MO disk structures have been used in commercial MO drives. With conventional MO disks it has not been possible to access information in magnetic domains when the incident laser beam laser beam covers more than one magnetic domain at a time. This limit is substantially proportional to the ratio of the wavelength of the laser beam to the numerical aperture (NA) of the optical elements used. In conventional prior art quadrilayer MO disk structures, therefore, recordation of magnetic domain marks smaller than the minimum incident optical spot size does not provide any benefit.
What is needed, therefore, is an apparatus and method that improves upon prior art access to, and storage of magneto-optical information.